The principal goal of this unit continues to be the biochemical characterization of eukaryotic and animal viral genes. Attention has been focussed on the segments of DNA and RNA Tumor virus genomes responsible for the establishment and maintenance of the transformed state. In this regard we have shown that the large form of polyoma tumor antigen plays no role in tumorigenesis mediated by polyoma DNA. SV40 DNA recombinants have been used to elucidate the mechanisms regulating the synthesis and processing of eukaryotic RNA. The first phase of risk assessment experiments conducted in the P4 facility at Ft. Detrick, Maryland, was recently completed. These studies showed that polyoma virus DNA is not transferred out of E. coli K-12 following the inoculation of susceptible newborn animals with bacteria containing recombinant plasmids or phage.